The present invention relates to a novel method and devices for measuring the cross-sectional dimensions of a thread-like or tape-like structure which is moving lengthwise, or variations of said dimensions, by means of a pair of spring-loaded members contacting said structure, and means for continually detecting the mutual distance of the contacting members and generating an electrical sensing signal.
Measuring and testing devices for continually detecting and assessing a cross-sectional dimension, such as the cross-sectional area or diameter of fast travelling textile yarns and other thread-like structures are generally known and in commercial use. Such devices are, by way of example, part of electronic yarn clearers on yarn winding machines which serve for eliminating thick and thin places of the yarn by means of a severing device.
Prior measuring devices of substantially inertialess operation are based on the capacitive or optoelectrical method for detecting the cross-sectional dimension of a travelling yarn. With both of these measuring devices, the sensing signal is dependent not only on the cross-sectional dimension of the yarn, but also on various interferences. With the capacitive method, the result is influenced by the dielectric properties of the yarn material which essentially depend upon the chemical nature and the humidity thereof. With the optoelectrical measuring method, the result is affected by absorption and reflection, in particular the colour of the material.
A so-called eveness tester is known where the yarn passes between a pair of rotatable rollers at a relatively low speed of, e.g., 12 yards per minute. One of the rollers is supported by a pivotable lever which is weight-loaded and thus held toward the other roller by gravity. The pivoting movements of said lever induced by the irregularity of the travelling yarn are transferred to an electromagnetic transducer through a micrometer which serves for zero adjustment. This eveness tester furnishes time average values of the yarn diameter, and thus is not suitable for detecting instantaneous values, in particular of yarns which travel at a high speed of 100 m/min or more. On the other hand, the result of such a measurement is independent of the optical and dielectrical properties of the yarn material.